Metal treatment apparatus

ABSTRACT

Molten metal equipment comprising a transportable vessel which is substantially airtight and has an enclosed duct extending from the vessel and communicating with its interior at two spaced positions below the normal level of the molten metal, a part of the duct being surrounded by a windowed magnetic core embraced by an induction coil. The enclosed duct is disposed on one side of the vessel and lies in a vertical plane like the handle of a mug. In one embodiment the vessel and duct are substantially airtight in themselves and at any connections between them. Alternatively they can be contained in a substantially airtight container.

United States Patent [72] lnventors John Christie Howard Curbar near Sheffield; Charles Peter Brittain, Whittington, both 01, England I [21] Appl. No. 680,827 [22] Filed Nov. 6, 1967 [45] Patented July 6,1971 [73] Assignee Associated Electrical Industries, Limited London, England [32] Priority Nov. 9, 1966 [331 GreatBi-itain [31 50258/66 [54] METAL TREATMENT APPARATUS 6 Claims, 2 Drawing Figs.

[52] U.S.C| 13/29, 266/34 [51] lnt.Cl H051) 5/14 [50] Field of Search 266/33, 34, 38, 39, 34 V; 13/29, 30

[56] References Cited UNlTED STATES PATENTS 2,423,912 7/1947 Tama et a1. 13/29 2,648,715 8/1953 Lillienberg 266/38 X Primary Examiner.l. Spencer Overholser Assistant Examinen-John S. Brown Attorney-Bowyer and Witherspoon ABSTRACT: Molten metal equipment comprising a transportable vessel which is substantially airtight and has an enclosed duct extending from the vessel and communicating with its interior at two spaced positions below the normal level of the molten metal, a part of the duct being surrounded by a windowed magnetic core embraced by an induction coil. The enclosed duct is disposed on one side of the vessel and lies in a vertical plane like the handle ofa mug. In one embodiment the vessel and duct are substantially airtight in themselves and at any connections between them. Alternatively they can be contained in a substantially airtight container.

PATENIEU JiiL a 197i FIGI METAL TREATMENT APPARATUS BACKGROUND OF THE INVENTION limb of a magnetic core which is also embraced by an inductor coil. Commonly the coil is on the same limb of the core asthat round which the loop passes, with the coil surrounding that limb between it and the loop. In operation molten metal occupying the duct or channel of the loop forms a secondary turn, short-circuited through the main body of molten metal in the furnace chamber, of a transformer the primary winding of which is constituted by the inductor coil. Application of alternating current to the primary inductor coil induces a heavy current in the short-circuited secondary turn of molten metal. This generates heat in the metal and at the same time sets up electromagnetic stirring forces. The structure defining the duct or channel of the loop, being a refractory structure usually encased in metal at least externally and sometimes also internally, may be integral with the furnace chamber structure or may, as in the arrangement described in our copending application No. 27741/65, British Pat. No. 1,154,903 be detachable from it. In this latter case the complete inductor unit comprising loop structure, core and coil may be detachable, or the loop structure, formed as an open-ended, e.g. U- shaped, structure may be separately detachable with the core and coil able to be left attached to the chamber structure. A detachable loop structure may, as in our said copending application, be constituted by a number of individually separable parts.

Holding furnaces and launders may likewise be provided with induction loops in order to maintain or control the temperature of molten metal in them.

SUMMARY OF THE INVENTION According to the present invention, which has the object of providing equipment which can be used for degassing of molten metal in a manner to be described later, there is provided a molten metal equipment comprising a substantially airtight arrangement of a refractory crucible or ladle provided with a refractory induction loop structure.

In accordance with a first aspect of the invention, the refractory crucible or ladle is provided with a substantially airtight lid and both the crucible or ladle and the induction loop structure are made substantially airtight not only in themselves, but also at any connections between them. In this respect, if the loop structure is built up of several separable parts, substantially airtight connections will also be made between these parts in order to ensure the required airtightness of the loop structure.

The refractory material both of the crucible or ladle structure and of the induction loop structure will usually be air permeable. To render such structures substantially airtight in themselves, therefore, it is contemplated that each of them may include an external metal casing and/or, when practicable, an internal metal lining. Joints between such casings or linings of the two structures can be made airtight by means of gasket or O-ring seals: either of these would be of heat resistant material or the joints would be water cooled.

Using equipment according to this first aspect of the invention for vacuum degassing, the induction coil and therefore the associated electrical apparatus, can be outside the vacuum system, thereby avoiding the known problems of electrical insulation in ambient conditions of vacuum pressure.

0 insulation.

In accordance with a second aspect of the invention, instead of making the crucible or ladle and the induction loop structure substantially airtight in themselves they may be contained in a substantially airtight container, for example in a vacuum bell or tank. In this alternative a lid for the crucible or ladle need not be airtight and indeed may be dispensed with. A larger vacuum pump would be required, and with the induction coil also contained in the enclosure, so that it would have to operate in vacuum, particular care would be required in its By substantially airtight is meant that in normal conditions of use, having regard to gaseous pressure differential between inside and outside and, in the case of the first aspect of the invention, to pressure head created by contained molten metal in the crucible or ladle and loop, air ingress to the molten metal will be prevented or at least minimized to a negligibly minute amount.

The induction loop structure is formed in a manner resem bling the handle of a mug and is disposed in a vertical plane to one side of the crucible or ladle with both ends of the duct or channel of the loop structure in communication with the interior of the crucible or ladle below the normal level of molten metal therein. For degassing, this same disposition of the loop is utilized and such disposition has been shown in the two embodiments of the invention illustrated by way of example in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 illustrates in partial cross section a substantially airtight transportable ladle with induction loop, while FIG. 2 illustrates a similar ladle and loop structure which, however, is not made airtight in itself but instead is wholly enclosed in a substantially airtight container.

DESCRIPTION OF PREFERRED EMBODIMENTS In both figures the ladle comprises a crucible 1 having a refractory lining 2 within an outer supporting metal casing 3. The ladle has a carrying yoke 4 secured to stub shafts 5 on opposite sides of the outer casing 3. A refractory induction loop structure 6 defines a C-shaped duct 7, the two ends of which communicate with the inside of the crucible l at two vertically spaced apart locations. The loop structure 6 is formed by three separate parts 8, 9 and 10, each comprising an outer sheath of nonmagnetic, metal tube such as 11 and a refractory lining such as 12. The adjacent cooperating ends of the parts 8, 9 and 10 are mitered, so that the end faces of their linings such as 12 and their sheathing tubes such as l 1 can firmly abut one another to ensure that no leakage of molten metal can occur from the duct 7 at the joints between the parts. The ends of the sheathing tubes have outwardly extending flanges such as 13 by which the parts 8, 9 and 10 can be secured together and to the crucible 1, preferably by means of quickly'detachable clamps 14. A windowed magnetic core 15 surrounds the lower limb of the duct 7 as formed by the part 10 and carries a winding 16 which is embraced by the loop structure 6 and is connectable to a suitable alternating current source. The core 15 may be split on a plane parallel to the plane of the drawing, with part of the core 15 mounted on a wheeled carriage 17 so as to be separable at the split from the remainder of the core, namely in a direction normal to the plane of the drawing. The resulting gap created at the split enables the ladle and loop structure to be removed vertically from the core through the gap. The same or another ladle can subsequently be lowered into position and the core reclosed round the lower limb of the loop structure.

With the ladle l-containing molten metal to a level higher than the upper limb (8), of the induction loop 6, energization of the winding 16 from a suitable alternating current source results in generation of heat in the metal occupying the duct 7 and also creates an electromagnetic stirring action which results in all of the molten metal in the ladle being heated.

In the arrangement of FIG. 1, the flange joints between the several parts of the induction loop 6 and between it and the ladle l are made substantially airtight by the provision of heat resistant sealing gaskets 18. The ladle 1 and loop 6 are themselves substantially airtight because of their metal casing 3 or sheaths 11. A lid 19 having a lifting lug 20 and a dr'awotf connection 21 closes the ladle l in a substantially airtight manner, for which purpose a sealing gasket 22 is provided between a peripheral flange 23 of the lid and a flange 24 provided round the top of the ladle l and secured in airtight manner, e.g. by welding, to its outer casing 3.

In the arrangement of FIG. 2, instead of providing the ladle l with a lid and airtight seals, the complete ladle and loop structure 1, 6, together with the core and winding 16, are contained in a substantially airtight container 25 having a drawoff connection 26. The lid 27 of this container is removably secured to it, with an intervening sealing gasket 28.

One way of using the airtight equipment of the invention for degassing molten metal, say liquid steel, is to draw a vacuum (via a drawoff connection such as 21 or 26 as the case may be) over the liquid steel in the ladle 1. Vacuum degassing per se presents difficulties because of excessive temperature loss during the process, which is necessarily long due to the slow migration of the gas upwards through the liquid metal into the low pressure region over it. However, by energizing the induction coil 16 on a magnetic core 15 linked with the loop structure 6, not only will heat loss be compensated, but alsothe circulation promoted in the liquid steel will lead to improved migration of contained gas. it is thus possible to provide an efficient but compact and relatively low cost vacuum degassing unit, with the possibility also of making such units of smaller capacity than hitherto practicable.

Another way of using the apparatus of the invention for degassing is to arrange for bubbles of inert gas to be passed up wards through the liquid steel (or other molten metal), either in the ladle l or in the loop structure 6 or both. Conveniently the inert gas can be introduced by way of the loop structure itself, and for this purpose the loop structure 6 in FIG. 1 has been shown as having a gas inlet connection 29. In addition to providing an inert gas cover over the molten metal, the bubbles of the inert gas entrain unwanted gases in the melt during their passage upwards through it, because of the low partial pressure of the unwanted gases in the bubbles.

We claim:

1. Molten metal equipment comprising:

a. a transportable refractory vessel such as a ladle;

b. a refractory duct extending outwardly from a vertical side of the vessel and having two ends communicating with the interior of the vessel at vertically spaced positions below the normal level of the molten metal in the vessel;

a windowed magnetic core surrounding a part of the duct; an induction coil embracing a part of the magnetic core;

e. airtight means enclosing the said vessel and the said duct;

and

f. wherein the said duct is in the form of a loop vertically disposed from said side and lying substantially in a vertical plane, as in the manner of a handle of a mug.

2. Equipment as claimed in claim 1, wherein the said vessel is provided with a substantially airtight lid and an airtight connection between said vessel and said duct.

3. Equipment as claimed in claim 1, wherein the said vessel and the said duct are rendered airtight by the provision of an external airtight metal casing, said casing surrounding both said vessel and said duct and conforming to the shapes thereof.

4. Equipment as claimed in claim 1, wherein the said induction coil which embraces the core is disposed outside of the airtight system formed by the vessel and the enclosed duct.

5. Equipment as claimed in claim 1, wherein the said vessel, the said duct, the said magnetic core and the said induction coil are contained in a substantially airtight container.

6. Equipment as claimed in claim 1, wherein the said magnetic core is formed of two se arable halves on a vertical line of separation, with one part 0 sald core being mounted on a wheeled carriage. 

2. Equipment as claimed in claim 1, wherein the said vessel is provided with a substantially airtight lid and an airtight connection between said vessel and said duct.
 3. Equipment as claimed in claim 1, wherein the said vessel and the said duct are rendered airtight by the provision of an external airtight metal casing, said casing surrounding both said vessel and said duct and conforming to the shapes thereof.
 4. Equipment as claimed in claim 1, wherein the said induction coil which embraces the core is disposed outside of the airtight system formed by the vessel and the enclosed duct.
 5. Equipment as claimed in claim 1, wherein the said vessel, the said duct, the said magnetic core and the said induction coil are contained in a substantially airtight container.
 6. Equipment as claimed in claim 1, wherein the said magnetic core is formed of two separable halves on a vertical line of separation, with one part of said core being mounted on a wheeled carriage. 